1. Field of the Invention
This invention relates to the reduction of noise in consumer electronics and, more particularly, to active noise cancellation.
2. Description of the Related Art
Active noise cancellation techniques are often used to reduce noise. Typically, active noise cancellation involves detecting the noise generated by a system and generating a responsive cancellation wave that will reduce or even eliminate the noise. Noise detection is typically performed using a microphone. The analog signal detected by the microphone is converted into a digital signal by an ADC (Analog to Digital Converter), which is processed by a DSP (Digital Signal Processor) to generate a compensating digital signal. The compensating digital signal is provided to a DAC (Digital to Analog Converter), which converts the digital signal into an analog signal for input to a speaker. While often effective, active noise cancellation techniques require expensive processing components and extensive hardware (e.g., microphones, ADC, DSP, DAC, speakers).
Consumer electronics contain numerous noise sources. For example, computer systems include components such as fans, power supplies, and disk drives, each of which may generate noise as it operates. However, these components may be critical to system functionality. Furthermore, given the size and/or cost of consumer electronics, it may be impractical or uneconomical to include typical active noise cancellation devices in consumer electronics. If conventional noise cancellation techniques are unavailable, designers of many consumer electronics are forced to balance necessary functionality such as cooling against noise. This trade-off may affect the performance, placement, size, life, serviceability, and support cost of the product if less functionality is provided in an attempt to reduce noise. For example, product improvements may be limited by the lack of a cooling fan in products in which a cooling fan is not currently an option due to the unacceptability of its noise. Many products that include fans are not optimal designs, have reduced features, or cost significantly more in order to keep fan noise within customer acceptable limits. Accordingly, new active noise cancellation devices are desirable for use in consumer electronics.
Various embodiments of a method and apparatus for providing associative noise attenuation are disclosed. In one embodiment, a system may include a memory configured to store an attenuation waveform and control logic. The control logic is configured to receive a synchronizing signal indicative of an operating characteristic of a noise source. In response to a value of a characteristic (e.g., frequency) of the synchronizing signal, the control logic is configured to output the attenuation waveform from the memory if the attenuation waveform is associated with that value of the characteristic of the synchronizing signal. An attenuating noise generated dependent on the attenuation waveform attenuates a noise generated by the noise source.
In some embodiments, the system may also include a DAC (Digital to Analog Converter) configured to generate an analog attenuation signal from a digital representation of the attenuation waveform stored in the memory. The system may also include an actuator configured to generate the attenuating noise in response to the analog attenuation signal from the DAC.
The memory may be configured to store digital representations of a plurality of attenuation waveforms. Each of the digital representations may be associated with a respective value of the characteristic of the synchronizing signal.
The attenuation waveform may be associated with a range of values of the characteristic of the synchronizing signal. The control logic may be configured to output the attenuation waveform from the memory if the value of the operating characteristic is within the range of values of the characteristic. The control logic may be configured to output the attenuation waveform from the memory if an associated value of the characteristic associated with the attenuation waveform is closer to the value of the characteristic of the synchronizing signal than any other associated values of the characteristic associated with other attenuation waveforms stored in the memory. The control logic may be configured to perform interpolation on the attenuation waveform dependent on a relationship between the value of the characteristic of the synchronizing signal and the associated value of the characteristic associated with the attenuation waveform.
The system may include a processing device configured to modify the attenuation waveform dependent on the value of the characteristic of the synchronizing signal prior to generation of the attenuating noise dependent on the attenuation waveform. For example, the processing device may be configured to adjust an amplitude of the attenuation waveform dependent on the value of the characteristic. Similarly, the processing device may be configured to adjust a frequency of the attenuation waveform dependent on the value of the characteristic of the synchronizing signal.
In one embodiment, the characteristic of the synchronizing signal may be the frequency of the synchronizing signal. The synchronizing signal may be a tachometer signal indicative of revolutions per unit time of a rotating component included in the noise source. Alternatively, the synchronizing signal may be indicative of an air density measured proximate to the noise source. In other embodiments, the synchronizing signal may be indicative of a system load of the noise source, wherein the noise source includes a power supply. The synchronizing signal may be a non-acoustic signal (e.g., the synchronizing signal may be indicative of a non-acoustical operating characteristic of the noise source).
An embodiment of a method may include: a memory storing an attenuation waveform; receiving a synchronizing signal indicative of an operating characteristic of a noise source; if the attenuation waveform is associated with a value of a characteristic of the synchronizing signal, outputting the attenuation waveform from the memory in response to receiving the synchronizing signal; and an actuator generating an attenuating noise dependent on the attenuation waveform in response to said outputting.